Many machines use hydraulic actuators to accomplish a variety of tasks, such as moving an implement. Examples of such machines include, without limitation, dozers, loaders, excavators, motor graders, and other types of heavy machinery. The hydraulic actuators in such machines are linked via fluid flow lines to a pump associated with the machine to provide pressurized fluid to the hydraulic actuators. Chambers within the various actuators receive the pressurized fluid in controlled flow rates in response to operator demands or other signals. The pump can be a load-sense hydraulic pump that, in response to the magnitude of the load acting on the implement, automatically varies the flow rate of the pressurized fluid. For example, when the implement encounters a heavy load, the load-sense hydraulic pump provides a correspondingly high flow rate to the hydraulic actuators. Likewise, when the implement encounters a small or light load, or when no load acts on the implement, the load-sense hydraulic pump provides a correspondingly low flow rate to the hydraulic actuators.
Oftentimes, after completing a task and when no load is acting on the implement, an operator may desire to dislodge dirt, mud, clay, or debris from the implement. To do so, the operator may quickly cycle a control lever back and forth, causing the hydraulic actuators to expand and retract, thereby moving the implement back and forth in rapid succession. This is sometimes referred to as rapid shakeout, or rapid sharing of the implement. However, because rapid shakeout is desired and typically occurs when no load is acting on the implement, e.g., when the bucket is substantially empty and when the load-sense pump is providing pressurized fluid to the actuators at a low flow rate, the actuators can respond slowly to the operator's commands.
Several known hydraulic systems having a load-sense pump have been adapted for accommodating rapid shakeout. One exemplary fluid system is disclosed in U.S. Pat. No. 5,235,809 for a Hydraulic Circuit for Shaking a Bucket on a Vehicle, filed on Sep. 9, 1991, and issued to Robert G. Farrell on Aug. 17, 1993 (“Farrell”). Fluid systems, such as disclosed in Farrell, include an implement such as a bucket operated by a hydraulic actuator, a directional valve for controlling fluid flow from a load sensing variable displacement pump, and a hydraulic bucket shake circuit. In this type of system, when an operator desires a rapid shakeout, the operator manually activates the hydraulic bucket shale circuit, which forces the pump to a maximum displacement condition. In this condition, the pump provides standby pressure and fluid flow to the hydraulic actuator by way of the directional valve so that the hydraulic actuator can rapidly expand and retract to rapidly shaking the bucket. However, it is a shortcoming to this system that manual activation is required for operation of the hydraulic bucket shake circuit. An additional shortcoming is that the hydraulic bucket shake circuit is a binary circuit that is either off or on for forcing the pump to a maximum displacement condition. This design can waste fuel and subjects the machine, including the pump and the engine, to unnecessary wear.
It should be appreciated that the foregoing background discussion is intended solely to aid the reader. It is not intended to limit the disclosure or claims, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use, nor is it intended to indicate any element to be essential in implementing the examples described herein, or similar examples.